Field of the Invention
The present invention relates to control of tracking a subject and moving a subject image to a predetermined position of an image or holding the subject image.
Description of the Related Art
A digital camera or the like in which exposure determination or focusing is automated and on which a controller that prevents image blurring of a captured image due to hand shake or the like is mounted is known. A detection function of detecting a subject's face or body has been proposed. For example, a pattern for determining a person' s face is determined in advance and a part corresponding to the pattern in an image is detected as the person's face. Information of the detected person's face image is referred to in focusing control, exposure control, or the like.
When a moving subject is photographed or when photographing is performed using a telephoto lens having a large focal distance, the following phenomena may occur. If a moving object serving as a subject deviates from an angle of view due to movement of the subject, a special technique is required of a photographer to accurately track the moving subject with only a manual operation. If an image is captured with a camera having a telephoto lens, image blurring due to hand shake increases and it is thus difficult to hold a main subject at the center of a captured image. If the photographer operates the camera to capture the subject in the angle of view again, image blurring is corrected depending on a degree of hand shake when the photographer intentionally operates the camera. Accordingly, it is difficult for a photographer to perform a micro adjustment operation to capture a subject in an angle of view due to an influence of image blurring correction control or to locate a subject image at the center of a captured image.
Japanese Patent Laid-Open No. 2010-93362 discloses an imaging device that automatically tracks a subject by moving a part of an optical system in a direction crossing an optical axis. A position of a subject is detected from an image signal acquired by an imaging element and a subject tracking computational load is calculated.
In a system that performs subject tracking control to hold an image position of a subject at a specific position on an image, there is a possibility that subject detection delay or detection accuracy will have a large influence on the tracking control. For example, in detection of a subject which is performed by analyzing a captured image, a detection delay with respect to real time necessarily occurs. Position feedback control is performed to hold an image position of a subject at a specific position in an angle of view. At this time, the feedback control has to be performed in consideration of a dead time due to the detection delay.
Subject tracking control of correcting an optical image of a subject by driving a shift lens or the like before the optical image is input to an imaging element is known. In this case, there is a possibility that a delay with respect to real time in detection of a subject will have a large influence on subject tracking performance. If a feedback gain is set to be large to enhance subject trackability, there is a possibility that tracking will oscillate depending on photographing conditions. On the other hand, if the feedback gain is set to be small so as not to oscillate, the subject trackability degrades and a subject is likely to be missed.